EP-A-0 576 728 discloses a method and an apparatus for opening centrally folded sheets which are conveyed in a stepwise manner in an imbricated formation, in which each sheet rests on the preceding sheet, by means of a clamp-type conveyor with pivotable clamps. The clamps retain the sheets at their folded edge, which trails with respect to the open edge located opposite it. An opening device with a suction head which can be raised and lowered is arranged to the side of the clamp-type conveyor. By virtue of the clamps being pivoted, the sheets are moved out of an imbricated formation, wherein the edge runs at right angles to the conveying direction, into an imbricated formation wherein the edge runs obliquely with respect to the conveying direction and in which, on the side facing the opening device, the sheets project beyond the adjacent sheets by way of a lateral corner region. As soon as the corner region of one sheet in each case has arrived at the suction head, the clamp-type conveyor is brought to a standstill, whereupon the suction head grips the top sheet part in the corner region and lifts it off from the bottom sheet part.
When the clamp-type conveyor is set in operation again, the suction head releases the lifted-off sheet part, which comes into abutment against a profile holding-open element. The clamps are then pivoted in the opposite direction, with the result that the open corner region, which is held open by means of the holding-open element, then becomes the leading corner. An acceleration conveyor grips the bottom product part in the leading corner region in order to deposit the open sheet on a saddle of a gatherer-stitcher. As a result of the stepwise transportation, operation is not smooth and the processing capacity may well be restricted. Furthermore, the design of the apparatus is complicated.
A method of, and an apparatus for, opening multi-sheet, centrally folded products by way of continuous conveying is disclosed in EP-A-0 344 787. A cam-type conveyor transports the products in an imbricated formation, in which each product rests on the preceding product, with the open edge leading with respect to the folded edge and running obliquely with respect to the conveying direction. An opening device with a plurality of suction-head pairs arranged one behind the other at the same spacing as the products is provided to the side of the cam-type conveyor. The suction-head pairs can be moved synchronously in and counter to the conveying direction in time with the printed products, and the suction heads of the suction head pairs can be moved towards one another, and away from one another, transversely with respect to the conveying plane. They grip in each case, the lowermost and the uppermost of the mutually abutting sheets in the lateral corner region and lift them off from the rest of the sheets. After the lifted-off sheets have been released, they come into abutment against directing elements, in order to be directed away above and beneath the following suction heads. The products are opened gradually in this manner in order then to be deposited on the saddle of a gatherer-stitcher. The gradual opening of the products need a considerable amount of time and requires a high-outlay opening device. The complicated movement of the suction heads, in turn, restricts the processing capacity.